Numerous processes have been proposed for imparting wrinkle resistance, shrinkage resistance and smooth-drying properties to fabrics and garments, made from cotton or other cellulosic fibers. The treated garments or fabrics retain their dimensions, smooth appearance and normal shape while being worn and after numerous cycles of domestic washing with an alkaline detergent in a washing machine and drying in a tumble dryer.
In many processes, a solution of formaldehyde or a formaldehyde adduct and an acidic catalyst is applied to the textile and the treated fabric or textile is heated to bring about crosslinking of the cellulose molecules of the textile. Owing to the toxicity associated with formaldehyde and its adducts, alternative methods of imparting durable press characteristics to cellulosics are of considerable interest.
Welch et al., in U.S. Pat. No. 4,820,307, herein incorporated by reference, have proposed a process for formaldehyde-free durable press finishing of cotton textiles, in which the textile is treated with a solution of a polycarboxylic acid at elevated temperatures. Catalysts for the process include alkali metal dihydrogen phosphates and alkali metal salts of phosphorous, hypophosphorous and polyphosphoric acids. Cotton fabrics, thus treated with citric acid as the polycarboxylic acid, using sodium dihydrogen phosphate catalyst, discolor significantly upon treatment at 180.degree. C. for 90 sec. The discoloration can be removed by post-treatment with various materials, of which the most effective are magnesium monoperoxyphthalate, sodium perborate, sodium borohydride, hydrochloric acid and sodium hypochlorite. Sodium tetraborate and boric acid are relatively ineffective for improving the whiteness of the fabrics.
Andrews, "Non-Formaldehyde Durable Press Finishing of Cotton with Citric Acid," 1989 International Conference and Exhibition, American Association of Textile Chemists and Colorists, pages 176-183, has proposed using citric acid, as at least a partial substitute for more expensive 1,2,3,4-butanetetracarboxylic acid, in compositions for imparting durable press properties to cellulosic fabrics. Yellowing of fabrics, treated with citric acid, is recognized as a problem, particularly in the case of treating solutions containing sodium dihydrogen phosphate or sodium hypophosphite catalyst, cured at 190.degree. C. or 200.degree. C. Use of lower curing temperatures resulted in generally improved whiteness indices, but decreased durable press ratings.
Welch et al., "Ester Crosslinks: A Route to High Performance Nonformaldehyde Finishing of Cotton," Textile Chemist and Colorist, vol. 21 (1989), pages 13-17, disclose using various polycarboxylic acids for the cross-linking of cellulosics. Sodium hypophosphite was judged the most effective catalyst for producing good durable press properties, without undue yellowing, even in the case of citric acid.
It is an object of this invention to provide an improved method for decreasing the yellowing of cellulosic fabrics, treated at a high temperature with one or more polycarboxylic acids in the presence of a phosphorus-containing catalyst.